Lithium-ion batteries have advantages of high energy capacity, long cycle life, and high efficiency, etc., and have been widely applied in consumable electronic devices, electric vehicles, and energy storage facilities. Currently, due to the reasons of government support, market demand, etc., the development of batteries with high energy density is imperative. A pouch battery becomes a product pursued in the industry, since the pouch battery has advantages of low cost, high energy density, and flexibilities during the assembly process in module.
Generally, a battery module includes a plurality of battery cells, and the battery cell is electrically connected to one another in series. In the prior art, a copper electrode tab and an aluminum electrode tab of the battery cell are connected together by bolting or ultrasonic welding, for the battery module of battery cells being pouch batteries. However, since a difference between a melting point of copper and aluminum is 424° C. and a difference between the coefficient of linear expansion of copper and aluminum is 40%, it is difficult to weld the two together; especially in automatic production, the production progress of the battery module is negatively affected; while for the manner of bolting, the reliability is poor, and more space is occupied, so that a volume energy density of the battery module is relatively low.